Patent GB-129312-A (GB)
Title: New or Improved Method of Directing a Route to a Pre-determined Destination Through an Unknown Country by Observation of either the Sun, Moon or Stars and an Instrument therefor.
Inventor: MARDEN BASIL JOCK NEWTON
IPC: G01C21/02
Filed: 1917-10-09
Abstract: 129,312. Marden, B. J. N. Oct. 9, 1917. Spherical-trigonometry calculators.-The invention comprises an azimuth-finder by means of which the azimuth at any time and date of the sun, the moon, or any one of a prearranged series of fixed stars may be calculated, and a compass, secured to the back of the azimuth-finder, for directing a route on the earth or through the atmosphere to a destination of known bearing by observation of the heavenly body of which the azimuth has been calculated. The azimuth-finder, Fig. 2, consists of a plate C with a circular aperture graduated according to the days of the year, a rotatable dial D provided with a number of circles d', d<2>, d<3>, &c. each for a particular latitude and graduated according to the hours of the day, and a central disk E carried by a strip F linearly adjustable in the plate C. The radii of the circles d<1> &c. are obtained by multiplying the tangent of the angle of latitude for which it is required by a suitable constant K<1>. The disk E is graduated according to a scale obtained by projecting equal divisions of a circle in the equatorial plane on to the plane of the horizon. One end of the strip F is graduated according to a scale obtained by multiplying the tangent of the angle of declination of the sun at the dates shown by the constant K<1> and the other end of the strip is similarly graduated for a number of fixed stars, the declinations of which are constant. The moon scale on the strip F is a plain scale of numbers and the required division is calculated for midnight on the requried date by multiplying the tangent of the declination angle by K<1>, a table so 'compiled being previously prepared. To obtain an azimuth of the sun, the strip F is adjusted to bring the required date on the scale into register with a datum-line C" on the plate C, and a thread or the like secured to the centre of the disk E is alined with the point on the circle d<1>, d<2>, or d<3> corresponding to the time of observation and crosses the scale on the disk E at a reading corresponding to the required azimuth. For use in obtaining star azimuths, the dial D is marked with the names of stars at points corresponding to the times at which the stars cross the meridian on the 1st of January of the year concerned, and to obtain the azimuth the dial D is first rotated until the name of the required star registers with the date of the observation on the plate C and the strip F is moved until the name of the star registers with the datum-line C<x>. For obtaining moon azimuths, the outer edge of the back of the dial D is graduated into 360 divisions and the scale is observed through an aperture in the back of the plate C in the centre line of the strip F. The dial D is then adjusted so that the scale reading visible at the back of the plate C corresponds to 180 minus the hour angle of the moon in degrees at midnight of the date of observation, the required number being obtained from a previously compiled table, 1 being added for every two hours after midnight and 1 substracted for every two hours before midnight. The strip is then adjusted and the reading taken as before. In order to ascertain the time of rising and setting of any body, a visibility strip, Figs. 4 and 5, is graduated in divisions according to scales obtained by multiplying the distances on the scales on the strip F by the square of the tangent of the angle of latitude. The slip is then applied to the plate C with its top and bottom edges in alinement with the edges of the plate C and the time of rising is read off on the right-hand side of the dial D and the time of setting on the left-hand side, the reading to be adopted on the scale in ascertaining the visibility of the moon being the corresponding declination moon number.